Messages in this thread | | | Date | Fri, 17 Apr 2020 11:26:24 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH v2] KVM/arm64: Support enabling dirty log gradually in small chunks |
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On 2020-04-17 10:46, zhukeqian wrote: > Hi Marc, > > On 2020/4/16 23:08, Marc Zyngier wrote: >> On Mon, 13 Apr 2020 20:20:23 +0800 >> Keqian Zhu <zhukeqian1@huawei.com> wrote: >> >>> There is already support of enabling dirty log graually in small >>> chunks >> >> gradually >> >>> for x86 in commit 3c9bd4006bfc ("KVM: x86: enable dirty log gradually >>> in >>> small chunks"). This adds support for arm64. >>> >>> x86 still writes protect all huge pages when >>> DIRTY_LOG_INITIALLY_ALL_SET >>> is eanbled. However, for arm64, both huge pages and normal pages can >>> be >> >> enabled >> >>> write protected gradually by userspace. >>> >>> Under the Huawei Kunpeng 920 2.6GHz platform, I did some tests on >>> 128G >>> Linux VMs with different page size. The memory pressure is 127G in >>> each >>> case. The time taken of memory_global_dirty_log_start in QEMU is >>> listed >>> below: >>> >>> Page Size Before After Optimization >>> 4K 650ms 1.8ms >>> 2M 4ms 1.8ms >>> 1G 2ms 1.8ms >> >> These numbers are different from what you have advertised before. What >> changed? > In patch RFC, the numbers is got when memory pressure is 100G, so the > number > is bigger here.
OK.
>> >>> >>> Besides the time reduction, the biggest income is that we will >>> minimize >> >> s/income/improvement/ >> >>> the performance side effect (because of dissloving huge pages and >>> marking >> >> dissolving > embarrassed for these misspell :(
No need to be embarrassed. I do a lot worse, at all times. That is why you and I need other people to review our patches and fix things! ;-)
>> >>> memslots dirty) on guest after enabling dirty log. >>> >>> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com> >>> --- >>> Documentation/virt/kvm/api.rst | 2 +- >>> arch/arm64/include/asm/kvm_host.h | 3 +++ >>> virt/kvm/arm/mmu.c | 12 ++++++++++-- >>> 3 files changed, 14 insertions(+), 3 deletions(-) >>> >>> diff --git a/Documentation/virt/kvm/api.rst >>> b/Documentation/virt/kvm/api.rst >>> index efbbe570aa9b..0017f63fa44f 100644 >>> --- a/Documentation/virt/kvm/api.rst >>> +++ b/Documentation/virt/kvm/api.rst >>> @@ -5777,7 +5777,7 @@ will be initialized to 1 when created. This >>> also improves performance because >>> dirty logging can be enabled gradually in small chunks on the first >>> call >>> to KVM_CLEAR_DIRTY_LOG. KVM_DIRTY_LOG_INITIALLY_SET depends on >>> KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (it is also only available on >>> -x86 for now). >>> +x86 and arm64 for now). >>> >>> KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the >>> name >>> KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs >>> that make >>> diff --git a/arch/arm64/include/asm/kvm_host.h >>> b/arch/arm64/include/asm/kvm_host.h >>> index 32c8a675e5a4..a723f84fab83 100644 >>> --- a/arch/arm64/include/asm/kvm_host.h >>> +++ b/arch/arm64/include/asm/kvm_host.h >>> @@ -46,6 +46,9 @@ >>> #define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3) >>> #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4) >>> >>> +#define KVM_DIRTY_LOG_MANUAL_CAPS >>> (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \ >>> + KVM_DIRTY_LOG_INITIALLY_SET) >>> + >>> DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use); >>> >>> extern unsigned int kvm_sve_max_vl; >>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c >>> index e3b9ee268823..1077f653a611 100644 >>> --- a/virt/kvm/arm/mmu.c >>> +++ b/virt/kvm/arm/mmu.c >>> @@ -2265,8 +2265,16 @@ void kvm_arch_commit_memory_region(struct kvm >>> *kvm, >>> * allocated dirty_bitmap[], dirty pages will be be tracked while >>> the >>> * memory slot is write protected. >>> */ >>> - if (change != KVM_MR_DELETE && mem->flags & >>> KVM_MEM_LOG_DIRTY_PAGES) >>> - kvm_mmu_wp_memory_region(kvm, mem->slot); >>> + if (change != KVM_MR_DELETE && mem->flags & >>> KVM_MEM_LOG_DIRTY_PAGES) { >>> + /* >>> + * If we're with initial-all-set, we don't need to write >>> + * protect any pages because they're all reported as dirty. >>> + * Huge pages and normal pages will be write protect gradually. >>> + */ >>> + if (!kvm_dirty_log_manual_protect_and_init_set(kvm)) { >>> + kvm_mmu_wp_memory_region(kvm, mem->slot); >>> + } >>> + } >>> } >>> >>> int kvm_arch_prepare_memory_region(struct kvm *kvm, >> >> As it is, it is pretty good. The one thing that isn't clear to me is >> why we have a difference in behaviour between x86 and arm64. What >> prevents x86 from having the same behaviour as arm64? > I am also not very clear about the difference. Maybe there is historic > reason. > > Before introducing DIRTY_LOG_INITIALLY_ALL_SET, all pages will be write > protected when starting dirty log, but only normal pages are needed > to be write protected again during dirty log sync, because huge pages > will > be dissolved to normal pages. > > For that x86 uses different routine to write protect huge pages and > normal pages, > and arm64 uses same routine to do this, so arm64 still write protect > all > pages again during dirty log sync, but x86 didn't. > > So I think that x86 can write protect huge pages gradually too, just > need to add > some code legs in dirty log sync.
Fair enough. It'd be good if you could investigate this as well. In the meantime, I'll queue this patch for a spin in -next.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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